WO 02/076150 A1 discloses an apparatus which controls multiple light sources of which the light is mixed to obtain light of a predetermined color light. A processor compares the amount of light detected of each of the light sources with a desired amount and controls drivers of the light sources such that the light sources produce the desired light level. The light sources are three strings of red, blue and green light emitting diodes (further also referred to as LED's), respectively. Each string of LED's is driven by a separate switched mode power supply (further also referred to as SMPS). The color of the mixed light is controlled by controlling a power supplied by the three SMPS's. In an embodiment, a common SMPS is arranged in front of the three SMPS's which drive the differently colored LED strings. It is a disadvantage of the prior art apparatus that three SMPS's are required to be able to drive the differently colored LED strings such that their color point can be controlled.